High-speed disc saw felling heads (DSFH) are commonly used to harvest trees. DSFHs typically include a large circular blade with a cutting diameter of 52 to 60 inches that is rotated continuously about a generally vertical axis at a high speed of approximately 1200 r.p.m. Replaceable teeth are mounted around the circumference of the blade. To cut a tree, the rotating blade is advanced toward and through the trunk of the tree at an elevation above ground level, and generally parallel to the ground, rotating about an axis that is generally parallel to the tree trunk.
Although driven by a motor such as a hydraulic motor, the rotational speed of the blade typically diminishes the longer the blade is cutting through any given tree. In order to keep the rotational speed sufficiently high that the blade is able to cut through a given tree in a single cut (e.g., without removing the blade from the tree to allow it to speed up again), the DSFH typically relies upon the high rotational momentum of the blade to keep the blade rotating for a sufficiently long time to cut through the tree.
In a feller buncher, during severance of the tree, the tree advances over the circular blade, as the vehicle is driven forward, and onto a butt plate. Hydraulically-actuated grapple arms then close around the tree, retaining it in a vertical attitude. This is sometimes referred to as a cut and catch operation. Several trees can be harvested and stored (bunched) in a vertical orientation before being dumped as a bunch into a pile ready for subsequent removal and processing. Piling groups of trees in this manner, rather than individually, improves harvesting efficiency. Fellers have also been used which only cut and do not accumulate or bunch the cut trees.
Although DSFHs allow for efficient harvesting of trees, the cutting action of the blade typically must occur within a horizontal plane (horizontal meaning generally perpendicular to the tree trunk) that is some distance above the ground. If the blade severs the trees closer to the ground, the blades of the DSFHs experience high rates of wear due to the erosive effects of earth and/or sand being propelled into the housing of the machine. Repairing such worn-out DSFHs is expensive.
Because the blades of the DSFHs must operate away from the ground, sizable stumps are left when trees are severed by the DSFHs. This is undesirable since large stumps can be unsightly, can delay the decomposition of the root systems of felled trees, and can cause a variety of other problems such as damage to the tires of other logging equipment, especially log skidders.
Due to the problems associated with leaving sizable stumps, the severing of trees by DSFHs often is followed by the use of stump grinding machines. These machines typically have a stump grinding drum rotated about a generally horizontal axis or teeth on a horizontal axis rotating disc that moves back and forth axially through the stump. While such machines are able to fragment the stumps or brush, stump grinding is not only expensive insofar as it constitutes a distinct, second operation that must be performed in the tree-felling process, but also is expensive insofar as the stump grinding machines themselves are expensive to rent/own and operate.
A known brush mulcher has teeth in two radially extending spiral patterns spaced 180° apart on the bottom of a rotating blade having teeth like a disc saw blade. The brush mulcher blade is typically lowered on top of the brush or brush stems to mulch them. It is conceivable that it could also be used for severing very small trees and mulching their stumps in a horizontal direction. However, it could not be efficiently used for combined tree harvesting and stump reduction in commercial logging operations.
It therefore would be advantageous if a new apparatus and method could be developed that simplified and reduced the costs associated with harvesting trees and reducing stumps. It would in particular be advantageous if the new apparatus and method allowed for the rapid severing and harvesting of trees in a manner that did not leave behind large tree stumps. It would further be advantageous if the new apparatus and method was relatively inexpensive and simple to implement.